Method and device for purifying exhaust air produced during wood processing

Abstract

A device for the purification of exhaust air produced during the processing of wood materials comprises a first circuit (A) having a scrubber ( 2 ), a mist eliminator ( 4 ) and a regeneration container ( 7 ). In order to strip the washing liquid from organic substances, a second circuit (B) is provided and serves to remove a sub-stream of the washing liquid from the first circuit (A) and supply it to a desorber ( 12 ). The washing liquid purified in this way is recirculated to the first circuit (A).

1 . A method for purifying exhaust air, in particular exhaust air from the processing of wood materials, comprising a first circulation and a second circulation, wherein the first circulation comprises the following steps:
 scrubbing the exhaust air with a scrubbing liquid;   separating the exhaust air and the scrubbing liquid;   removing solids from the scrubbing liquid; and   recirculating the scrubbing liquid for scrubbing the exhaust air,
 wherein the second circulation comprises at least the following steps: 
   feeding the scrubbing liquid to a desorber;   removing organic substances from the scrubbing liquid in the desorber by a stripping gas which is carried in co-current or countercurrent with the scrubbing liquid, wherein the stripping gas is loaded with the organic substances,   wherein at least a substream of the scrubbing liquid is withdrawn from the first circulation and fed to the second circulation, and   wherein organic substances are removed from the scrubbing liquid in the second circulation, and the scrubbing liquid is at least partially recirculated to the first circulation after removal of the organic substances.   
     
     
         2 . The method as claimed in  claim 1 , wherein the exhaust air and the scrubbing liquid are separated in a wet electrostatic filter. 
     
     
         3 . The method as claimed in  claim 1 , wherein the co-current or countercurrent is adjusted such that, after leaving the desorber, the loaded stripping gas has a higher concentration of organic substances than the exhaust air. 
     
     
         4 . The method as claimed in  claim 1 , wherein, after leaving the desorber, the loaded stripping gas is fed to a thermal treatment or incineration. 
     
     
         5 . The method as claimed in  claim 1 , wherein the stripping gas is preheated before being loaded with the organic substances in the desorber. 
     
     
         6 . The method as claimed in  claim 5 , wherein a portion of the preheated unloaded stripping gas is mixed with the loaded stripping gas during or after leaving the desorber to reduce the water vapor concentration of the loaded stripping gas. 
     
     
         7 . The method as claimed in  claim 1 , wherein the scrubbing liquid is heated before entering the desorber. 
     
     
         8 . The method as claimed in  claim 7 , wherein the scrubbing liquid, before entering the desorber, is brought into thermal contact in a heat exchanger with the scrubbing liquid leaving the desorber, to heat the scrubbing liquid fed to the desorber and to cool the scrubbing liquid leaving the desorber. 
     
     
         9 . The method as claimed in  claim 1 , wherein at least a portion of the second circulation is rinsed periodically with a rinsing liquid. 
     
     
         10 . The method as claimed in  claim 9 , wherein the rinsing liquid is heated before rinsing. 
     
     
         11 . A device for purifying exhaust air, in particular exhaust air from the processing of wood materials, with a first circulation and a second circulation, wherein the first circulation comprising at least the following elements:
 a scrubber for scrubbing the exhaust air with a scrubbing liquid;   a droplet separator to separate the exhaust air and the scrubbing liquid after scrubbing;   a reprocessing container to collect the separated scrubbing liquid and to remove solids from the scrubbing liquid; and   a feed device to return the scrubbing liquid from the reprocessing container to the scrubber, and   wherein the device has a second circulation, comprises at least the following elements:   a withdrawal line to withdraw at least a substream of the scrubbing liquid from the first circulation;   a desorber for removing organic substances from the scrubbing liquid withdrawn, through a stripping gas carried in co-current or countercurrent with the scrubbing liquid; and   a recirculation line for returning the scrubbing liquid at least partially to the first circulation after removal of the organic substances.   
     
     
         12 . The device as claimed in  claim 11 , wherein the droplet separator is designed as a wet electrostatic filter. 
     
     
         13 . The device as claimed in  claim 11 , having a heat exchanger to preheat the stripping gas before it is loaded with the organic substances in the desorber. 
     
     
         14 . The device as claimed in  claim 13 , having a bypass device to mix a portion of the preheated unloaded stripping gas with the loaded stripping gas during or after leaving the desorber. 
     
     
         15 . The device as claimed in  claim 11 , wherein the second circulation comprises a heat exchanger having a first side and a second side, which is in thermal contact with the first side, wherein the scrubbing liquid fed to the desorber is conducted through the first side, and wherein the scrubbing liquid leaving the desorber is conducted through the second side, for heating the scrubbing liquid fed to the desorber and for cooling the scrubbing liquid leaving the desorber. 
     
     
         16 . The device as claimed in  claim 11 , wherein the device comprises at least one of a rinsing liquid feed and shut-off elements to rinse at least a portion of the second circulation with a rinsing liquid. 
     
     
         17 . The device as claimed in  claim 11 , which also has a funnel for feeding the stripping gas to a thermal aftertreatment or incineration after leaving the desorber. 
     
     
         18 . The method as claimed in  claim 1 , wherein the scrubbing liquid is a water-based scrubbing liquid. 
     
     
         19 . The method as claimed in  claim 1 , wherein the desorber is a column desorber. 
     
     
         20 . The method as claimed in  claim 1 , wherein the stripping gas is air. 
     
     
         21 . The method as claimed in  claim 3 , wherein the loaded stripping gas has a concentration at least five times higher than the exhaust air. 
     
     
         22 . The method as claimed in  claim 9 , wherein the rinsing liquid is a water-based rinsing liquid. 
     
     
         23 . The device as claimed in  claim 11 , wherein the desorber is a column desorber. 
     
     
         24 . The device as claimed in  claim 16 , wherein the device has a heat exchanger to heat the rinsing liquid.